What Can Go Wrong in an Email Migration (and How to Avoid It)

Migrating email — whether between providers, into Microsoft 365 for the first time, or during a company merger or rebrand — is well-understood, routine work for anyone who does it regularly. That doesn't mean it's risk-free. Because email is so visible and so immediate, small oversights during a migration tend to cause disproportionately noticeable disruption compared to their size.

Mail flow interruption during the switch

The most common visible problem is a gap, however brief, where incoming email either bounces or gets delayed while DNS records (the settings that tell the internet where your email should be delivered) are updated and propagate. DNS changes aren't instant everywhere at once, which is why migrations are typically planned to run both the old and new systems in parallel for a period, rather than switching everything off and on in one step.

Missing historical email or calendar data

Depending on the migration method used, older emails, folders, or calendar entries can sometimes fail to transfer completely, particularly from unusual folder structures, shared mailboxes, or very large mailboxes. A proper migration plan includes checking what actually transferred against what existed beforehand, not just assuming the tool handled everything.

Broken distribution lists and shared mailboxes

Shared mailboxes and distribution lists are easy to overlook because they don't belong to one obvious person, which means they're also easy to forget to test properly after a migration. Nothing is more awkward than discovering, two weeks later, that the "info@" mailbox has quietly stopped receiving anything.

Devices and apps not updated with new settings

Phones, tablets, and any third-party apps connected to the old email settings need updating separately after a migration — they don't automatically follow the change. It's easy to migrate the core system cleanly and then have individual staff struggling for days because their phone is still configured for the old setup.

Underestimating how much needs testing

A migration that "looks complete" based on a quick check of one inbox is different from one that's actually been tested properly — sending and receiving from multiple accounts, checking shared mailboxes, confirming calendar invites still work correctly, and checking mobile access, before declaring it genuinely finished.

Plan it properly rather than rushing it

None of these problems are unusual or hard to avoid with proper planning — they mostly come from treating a migration as a quick technical switch rather than a project with its own checklist.

If you're planning a migration — to Microsoft 365, away from it, or between providers — and want it done properly with minimal disruption, our Microsoft 365 & Cloud page covers how we can help, or get in touch.